Study Shows Car Crashes Rise With Daylight Savings Time

An economist has a warning for the more than 1.5 billion people living in countries that observe daylight saving time: Springing forward may be bad for your health. The wisdom of moving clocks an hour forward during summer months has long been a subject of debate. Proponents argue that extending daylight into the evening saves electricity, encourages people to exercise after work and reduces crime and traffic fatalities. Opponents say the costs of disrupting people’s schedules and sleep may outweigh the benefits. The available research offers fodder for both sides. Studies have supported the arguments on crime, exercise and fatalities, but cast doubt on the energy savings and suggested that the disruptions might increase the risk of heart attacks.

Austin Smith, a PhD candidate at the University of Colorado-Boulder, presented a paper at the annual meeting of the American Economic Association. He looked at national data on all fatal car crashes from 2002 to 2011 to see what happens immediately after people reset their clocks in the spring and fall. He does so by comparing the number of crashes that occur just before and after the time changes in each year, and also by comparing crashes on dates that — thanks to a 2007 policy change — fell within daylight saving time in some years and not in others.

The result: Fatal crashes increased by about 6 percent over the six days immediately following the spring transition, but didn’t change after the fall transition. Because people “lose” an hour only in spring, and because the accidents weren’t concentrated at times when changes in daylight might have been a factor, Smith attributes the spike in crashes to inadequate sleep. He estimates that the 6 percent increase amounted to more than 300 added deaths over the 10-year period he studied.

The research doesn’t demonstrate that daylight savings time is, on net, a killer. As Smith writes, the “result should be viewed as one piece of the puzzle, to be examined in conjunction with research on other impacts.” That said, it might make sense to take care on the road when the time comes to move clocks forward.